This invention relates to a power-operated focusing mechanism for a camera, and to an automatic focusing camera utilizing such mechanism.
Before photographing a subject, the lens of a variable lens camera must be axially displaced to a position at which the subject is brought into focus; this axial position being a function of the distance of the subject to the camera lens. While such function, hereinafter termed the lens/subject function, depends on many parameters associated with the optical system, one of its more important characteristics for purposes of the present discussion is its highly non-linear nature. In general, the slope of this function is greatest for close subjects and decreases assymtotically to zero for objects remote from the camera.
In order to properly set the axial position of the lens, it is conventional to mechanically couple the output arm of an optical range finder to the lens mount through a cam system into which the lens/subject function has been incorporated whereby operation of the range finder imparts proper displacement to the lens. In a different approach to powered displacement of the lens mount, the lens/subject function may be generated electrically. An example of the latter arrangement is illustrated in U.S. Pat. No. 3,522,764 which discloses an arrangement in which the setting of the lens is related to an acoustic range finder that produces a range pulse whose duration is directly related to the distance of the subject to the lens. The range pulse is used to control a power-operated focus mechanism that moves the lens to an axial position in which the subject will be in focus. The lens/subject function in this patent is developed in an analogous manner by a highly non-linear potentiometer which while generally satisfactory, can be expensive to manufacture and is not easily adapted to different lens systems since a different potentiometer has to be used with each different lens mount arrangement. As a consequence, a power-operated focus mechanism based on this principal of operation lacks a degree of flexibility.
It is therefore an object of the present invention to provide an improved power-operated focus mechanism.
Another object is to provide an economical power driven focus mechanism for a photographic camera.
A further object is to provide an automatic focusing camera.
A still further object is to provide an improved method of determining a lens position in accordance with subject distance.
Still another object is to provide a method of electrically generating a lens position responsive to subject distance ranging.
A further object is to provide a new and improved power-operated focus mechanism for a camers which eliminates analog computational components and techniques, and employs, instead, more versatile digital components for developing an arbitrary lens/subject function.